Fluid Recirculating Economizer

ABSTRACT

A flue gas heat recovery device is described. The device includes a packing tower. The packing tower is adapted to receive a flue gas stream. The packing tower also contains at least one water inlet, a water collection reservoir and a packing tray positioned between the inlet and reservoir. An air induction assembly may be attached to the packing tower or the inlet. A fuel gas line is in thermal communication with the reservoir. The fuel gas line has two ends a first end in close spatial relationship to a distal end of said reservoir, and a second end in close spatial relationship to a fuel output. Finally, a fluid conduit connects the second end of the fuel gas line and the water inlet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of US. Provisional Application Ser. No. 61/368,767 filed on Jul. 29, 2010, currently pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to furnace and boiler flue-gas economizers, and more particularly, this invention relates to a system of recovering flue effluent heat within a closed loop to equalize the temperature of a fuel line.

2. Background of the Invention

Furnaces or boilers combust fuel to melt ore, heat air, dry wood, or cook food. These activities generate high-temperature effluent, such as flue gas. This effluent contains wasted heat energy.

“Economizers” attempt to re-capture heat from effluent.

For example, U.S. Pat. No. 1,795,909 to Brunt et. al. describes a series of complicated flue-gas passages, dust catching channels, and other convoluted physical structures designed to pre-heat air. The '909 patent relies on these structures to transfer heat from the flue gas to cold air. Consequently, Brunt uses a number of complex heat sinks. Further, Brunt admits that “dust-catching” means are required for particulate, inasmuch as build-up around the heat-sinks is a problem.

Another economizer is shown in U.S. Pat. No. 4,318,366 to Tompkins. This economizer includes dispersal of heat-trapping fluid in the flue-gas. However, the Tompkins system requires strict control of the temperature of flue-gas at several points, as well as single use and strict control of the temperature of the heat-trapping fluid.

A need exists in the art for a flue-gas economizer which is not complicated in design. The economizer should rely on inexpensive heat trapping media which is automatically recycled after it absorbs and releases energy. The heat trapping media should be the only moving element throughout the economizer.

SUMMARY OF INVENTION

An object of the present invention is to provide a device which eliminates many of the drawbacks of state of the art heat economizer systems.

Another object of the invention is to provide a means to extract and recycle heat from combustion effluent that would otherwise be released into the atmosphere. A feature of the invention is a heat exchange region in which reusable fluid transfers heat, via thermal conductance, from flue gas and then eventually to fuel. An advantage of the invention is that the fluid is not in fluid communication with the fuel, and as such, neither contaminates, nor is contaminated by, the fuel.

Still another object of the invention is to maximize the efficiency of a boiler or a furnace charged with gas or liquid fuel. A feature of the invention is the use of a completely separate device to transfer heat energy from combustion flue-gas (which is generated by the boiler or furnace) to pre-combusted fuel so as to preheat the fuel. An advantage of the invention is that the preheated fuel feature increases the efficiency of the boiler or furnace as compared to if the fuel was not preheated

Yet another object of the present invention is to provide a flue-gas economizer which recycles heat exchange fluid. A feature of the economizer is that the heat transfer fluid is reused and confined within a recirculation loop so as not to contaminate or clog other aspects of the combustion system, such as fuel supply lines or effluent stacks. An advantage of the invention is that the economizer works independently of boilers, furnaces, and internal combustion devices generally.

A further object of the invention is to transfer energy from a heat exchange fluid to a pre-combusted fuel fluid. A feature of the invention is a jacket encircling a fuel gas line, where the jacket is adapted to receive the heat exchange fluid. An advantage of the invention is that it maximizes the surface area of contact between the fuel conduit line and the heat exchange fluid (thereby allowing for high rates of flow of heat exchange fluid) while preventing direct physical contact of the fuel to the heat exchange fluid.

Another object of the invention is to collect heat from large volumes of effluent emanating from a combustion process. A feature of the invention is that heat transfer occurs without constraining the volume of the effluent or increasing back pressure to the combustion process gas. An advantage of the invention is that it may be used in conjunction with high-pressure boilers and furnaces which expel large quantities of flue gas.

Yet another object of the invention is to increase the temperature of a fuel line before a change in fuel pressure. A feature of the invention is that it can be used to heat a fuel line before or after a reduction in fuel pressure. An advantage of the invention is that it is separate from a combustion system such that it can be situated intermediate the combustion system and the fuel supply line undergoing a pressure change. Another advantage is that residual heat from a combustion system can be utilized by the invention to prevent fuel lines from freezing.

Another object of the invention is to facilitate cleaning of the economizer. A feature of the invention is that a cleaning cycle may be operated to rid the system of waste product. An advantage of the invention is that the cleaning cycle may be operated at any time, even when the underlying boiler or furnace is operating.

Another object of the invention is to provide an economizer which may be used in conjunction with a natural draught burner. A feature of one embodiment of this invention is that a fan is used to create a pressure differential within the system. An advantage of the invention is that the burners of the natural draught burner are provided with sufficient air to support combustion.

A further feature of the invention is to provide an economizer where the life-span of any fan used within the system is maximized. A feature of one embodiment of the invention is that the fan does not contact any fumes. An advantage of the invention is that the lifespan of the fan is maximized inasmuch as the fan is not exposed to a caustic environment.

Yet another object of the invention is to provide an economizer which may be used with any kind of boiler or furnace without modifying the furnace. A feature of one embodiment of the invention is an air induction fan may be located at several alternate sites depending on the type of boiler attached thereto, removing the need to induce an air draught within the boiler itself. An advantage of the invention is that it does not require the addition of an air inducer into the furnace, by creating a stand-alone air induction unit within the economizer.

Briefly, the invention provides a flue gas heat recovery device comprising: a packing tower adapted to receive a flue gas stream; wherein said packing tower contains at least one water inlet, a water collection reservoir and a packing tray positioned intermediate said water inlet and said reservoir; a fuel conduit in thermal communication with the reservoir, wherein the fuel conduit has a first end in close spatial relationship to a distal end of said reservoir, and a second end in close spatial relationship to a fuel output; and a fluid conduit having a first end in fluid communication with an exterior surface of the fuel gas line and a second end in fluid communication with said water inlet.

The invention also provides a method for recovering heat from flue effluent, the method comprising contacting the effluent with a heat transfer fluid for a time sufficient to transfer heat from the effluent to the heat transfer fluid; transferring heat from the now heated heat transfer fluid to a fuel gas so as to heat the gas and cool the heat transfer fluid; combusting the now heated fuel gas which leads to the production of additional flue effluent; and repeating the process using now cooled heat transfer fluid and additional flue effluent.

BRIEF DESCRIPTION OF DRAWING

The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawings, wherein:

FIG. 1 depicts a cut-away side view of an economizer, in accordance with features of the invention;

FIG. 2 is a view of FIG. 1 taken along lines 2-2;

FIG. 3 is a cut-away side view of an alternate embodiment of an economizer, in accordance with the features of the invention;

FIG. 4 is a detailed view of FIG. 3 area 4-4 of one embodiment of the invention;

FIG. 5 is a cut-away side view of another alternate embodiment of an economizer, in accordance with the features of the invention; and

FIG. 6 is a detailed view of FIG. 5 area 6-6 of one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings.

Turning to FIG. 1, the device 10 broadly comprises a packing tower 30, disposed in a generally vertical position, and a heat transfer jacket 64 in fluid communication with said packing tower 30. In the embodiment shown, the heat transfer jacket 64 is positioned at approximately a 90 degree angle to the packing tower so as to be disposed in a generally horizontal direction. A recirculation pump 50 is connected to said heat transfer jacket 64.

Hot exhaust generated from a combustion process occurring in a furnace or boiler is directed to a first end 34 of the packing tower 30. While the packing tower 30 is filled with hot exhaust, a heat transferring fluid enters the second end (in this embodiment the top end) 35 of the packing tower 30 so as to be gravity-fed towards the first end 34 of the packing tower 30. As the heat transferring fluid traverses downwardly through packing media 32 positioned intermediate the first and second ends of the tower, the temperature of the heat transfer fluid is increased as it cools the hot exhaust permeating upwardly from the first end 34.

Upon draining or otherwise exiting the packing tower 30 through a means of egress or tower to jacket connection point 52, the heat transferring fluid enters and substantially fills the volume defined by an annular space created by an outer skin 63 of a heat jacket 64, and an exterior surface of a fuel conduit or line 66. This facilitates transfer heat from the now heated fluid to fuel traversing the conduit 66. Following traversal of the heat jacket 64, the now cooled heat transferring fluid is pumped by the fluid or recirculation pump 50 back to the second end 35 of the packing tower 30 to be re-circulated through the packing tower 30 which contains tower packing media 32.

Packing Tower Detail

In one embodiment, the packing tower 30 comprises a cylindrical structure, although other shapes are envisioned. In one embodiment, the packing tower is the vertical exhaust or smoke stack of a production environment or the portion of a vertical smoke stack.

The second end 35 of the packing tower 30 incorporates an exhaust aperture 36. In the embodiment shown in FIG. 1, said exhaust aperture 36 is open to the atmosphere. Exhaust aperture 36 may further incorporate one or more means of attaching exhaust handling devices, such as particulate scrubbers, negative pressure means, such as exhaust fans, and the like (not shown) for downstream processing of exhaust.

The interior of the packing tower 30 contains a plurality of packing media 32. Said packing media 32 is disposed between the first and second ends of the packing tower 30. In one embodiment, the shape of said packing media is mostly cylindrical and/or other hollow geometric shapes with stamped protrusions on the inside. The stamped protrusions allow for maximum heat exchange between the packing media, the effluent permeating upwardly through the media and the heat transfer fluid permeating downwardly through the packing media. In one embodiment, the packing media elements are metallic in construction, having a diameter of about 1″ and being approximately 1.25″ tall. However, other sizes are envisioned to maximize heat transfer and control back pressure. In one embodiment, the packing media 32 is placed on a fabricated packing tray 37 made from expanded metal, which is sheet metal having diamond-shaped holes stamped there through leaving a grid of approximately ⅛ inch of material remaining. The size of the apertures formed in the expanded metal tray is selected so as to prevent packing media 32 from falling through said apertures.

The packing media 32 is designed to provide maximum surface area for heat exchange fluid to contact the packing media 32. The maximum surface areas also allow the packing media 32 to transfer heat from the hot exhaust inasmuch as maximum surface area increases the time that both exhaust and heat exchange fluid contact the packing media 32. However, the packing media 32 are not so dense as to inhibit the transit of the hot exhaust through the packing tower 30. In one embodiment, the packing media 32 weighs 13 pounds while dry. The weight and quantity of packing media is selected to compensate for pressure loss and to optimize heat transfer. Further, the packing media is arranged such that heat exchange fluid does not pool or collect in any typographical features of the packing media 32.

A heat exchange fluid nozzle 40 is disposed between the second end of the packing tower 30 and the packing media 32. In the embodiment of the device depicted in FIG. 1, the nozzle 40 is disposed in the middle of a horizontal plane which runs parallel to the exhaust aperture 36, so as to facilitate downward projection of the heat transfer fluid (such as water) onto the packing media 32.

In another embodiment, not shown, the nozzle 40 is attached to the side of the wall of the packing tower 30 such that the nozzle is not adversely affected by the hot exhaust traversing the packing tower 30. In yet another embodiment, also not shown, more than one nozzle is employed.

During operation of the device 10, heat exchange fluid (such as water) exits the nozzle 40 and percolates downwardly through or otherwise traverses the packing media 32. In the embodiment shown in FIG. 1, the heat exchange fluid is propelled by the application of pressure and also by action of gravity. In other embodiments, the heat exchange fluid is propelled solely by action of pressure. In yet other embodiments, only gravity is responsible for the percolation.

Disposed between the first end of the packing tower 30 and the packing media 32 is the hot exhaust inlet 20. In one embodiment, the hot exhaust inlet 20 is in fluid communication with the headspace of a combustion chamber, such as those chambers found in furnaces and boilers. As such, the inlet serves as a means of ingress of combustion effluent into the device 10. While in some embodiments of the invention, the device 10 is connected to immobile devices such as large-scale boilers, in other embodiments, the hot exhaust inlet 20 connects to a temporarily-installed device, such as a generator.

Positioned superior from the hot exhaust inlet 20 is a gas and fluid permeable packing tray 37. Said packing tray 37 suspends and otherwise holds packing media 32 in place above the region of the tower receiving the hot flue gas. As such, the tray suspends the media above the head space. The hot exhaust is therefore in contact with packing media immediately upon entering the packing tower 30.

In one embodiment, the internal surfaces 38 of the packing tower 30 are substantially smooth. In another embodiment, the internal surfaces 38 of the packing tower 30 define a series of corrugations or channels designed to maximize the heat transfer characteristics of the said tower walls. The channels further provide a means for anchoring the packing media 32.

In one embodiment, the exterior of the packing tower 30 is insulated to prevent heat loss to the outside environment.

Finally, at the first end of the packing tower 30, the tower to jacket connection point 52 forms a heat transfer fluid exit conduit which provides the drainage means or other fluid egress means to facilitate removal of heat transfer fluid from the tower to the heat transfer jacket 64 described below.

Transfer Jacket Assembly Detail

The transfer jacket assembly comprises a sleeve or jacket 64 encapsulating, a fuel line 66. Specifically, the transfer jacket 64 resembles a tube radially displaced around a fuel conduit such that longitudinally extending portions thereof encircle or otherwise encase exterior surfaces of the fuel line 66 to form an annular space. The encasement of the fuel line 66 results in a void defined by the annular space, a fluid means of ingress (which is the heat transfer fluid exit conduit or tower to jacket connection point 52) situated at a first end of the void and a fluid means of egress (such as a connection conduit to pump inlet 56) situated at second end of the void. Further, in one embodiment of the invention, the exterior of the transfer jacket 64 is insulated so as to prevent heat loss to the external atmosphere. However, the external surface of the fuel line 66 is not insulated allowing for heat exchange between the interior of the transfer jacket 64 and the interior of the fuel line 66.

In one embodiment, the fuel line 66 is downstream of a fuel distribution network. In such a network (not shown) large quantities of fuel are sent over long distances using high-pressure transmission pipes. In one embodiment, such high pressure pipes contain fuel gas at 1200 psi. Upon reaching an end point of the network, such as a township, or a private user such as an industrial facility, the fuel gas line pressure is lowered to a pressure (e.g., 80 psi) suitable for end users. If the fuel gas line is not heated before the change in pressure, the fuel line would freeze once the pressure is decreased. In this embodiment, the fuel line 66 is positioned in close spatial relationship to that portion of the distribution network that subjects the fuel to depressurization so that the flange is adapted to receive or mate with a valve (not shown) separating the high pressure line from the fuel line 66.

In another embodiment, not shown, the fuel line 66 receiving heat within the transfer jacket 64 is the high-pressure transmission pipe prior to the decrease in pressure. Inasmuch as the fuel in the high-pressure line receives the heat from the heat transfer jacket, upon decreasing pressure, the lower pressure line is not liable to freeze. However, in this embodiment, the high-pressure transmission pipe must be designed to withstand not only the high-pressure fuel, but also the heated high pressure fuel which increases the pressure within the high-pressure line.

Finally, in further embodiments, the fuel line 66 is the upstream line side of the heater, and alternatively on the downstream line side of the heater.

In one embodiment, a first end or fuel output end 60 of the fuel line 66 is connected to a fuel-using device such as a furnace or a boiler. A second end or fuel input end 62 of the fuel line 66 is connected to a distribution line, or a still pressurized municipal gas supply or a fuel tank (not shown). The device 10 is capable of using any fuel, so long as the fuel may be conveyed in a fuel line, such as the fuel line 66 depicted in FIG. 1. The fuel must be of a type capable of being heated safely via thermal conductance and without significant expansion so as to rupture the fuel line 66. Fuels that have been safely used with this system include liquefied petroleum gas, methane, propane, butane, and higher carbon fuels which are liquids.

Inasmuch as in one embodiment, fuel is consumed at the first end 60 and originates at the second end 62, the fuel moves towards the first end 60 and away from the second end 62, which is the direction shown by the arrow gamma (“Γ”) in FIG. 1.

The heat transfer jacket 64 comprises two ends, a first end and a second end, which correspond to the two ends 60, 62 of the fuel line 66. However, in at least one embodiment, the heat transfer jacket 64 does not completely encapsulate the fuel line 66 and therefore a gap exists between the first end of the fuel line and the first end of the jacket (as well as the second end of the fuel line and the second end of the jacket) wherein the fuel line 66 remains exposed. Such a gap allows for direct manipulation of the fuel line 66 and facilitates the connection of the fuel line 66 to either a furnace or a fuel source.

The heat transfer jacket 64 is connected to a depending end of the heat transfer fluid exit conduit 52, which as discussed supra resides inferior to the packing tower 30. Proximate to the second end of the transfer jacket 64 is a pump inlet 56. The pump inlet 56 connects the interior of the heat transfer jacket 64 to a recirculation pump 50. The recirculation pump 50 applies negative pressure on the inlet 56.

Consequently, heat transfer fluid is drawn from the second end 35 of the packing tower, through the heat transfer fluid exit conduit 52, and to the pump inlet 56. Therefore, as shown in the embodiment of FIG. 1, the heat transfer fluid will travel in the direction depicted by arrow omega (“Ω”).

Inasmuch as the direction of the fuel “r” is opposite of the direction of the transfer fluid flow “Ω” the amount of time that fuel will be in thermal communication with (separated only by a wall of the fuel line 66) the temperature transfer fluid will be maximized.

The packing tower 30, transfer jacket assembly, and the recirculating pump 50 are connected through a series of conduits or piping described below.

Connection Detail

The second end 65 of the heat transfer jacket 64 is in fluid communication with the second end 35 of the packing tower 30. The first end 34 of the packing tower 30 is in turn connected to the first end of the heat transfer jacket 64. Consequently, the packing tower 30 and the heat transfer jacket 64 define a continuous loop to facilitate cycling of the heat transfer fluid.

Heat transfer fluid such as water is introduced at the recirculation pump 50. Heat transfer fluid exits the recirculation pump 50 through the pump outlet 58 to be fed under pressure to the second end 35 of the tower. The pump outlet 58 is in turn connected to one end of external fluid conduit 46 which lies external to the tower 30. The heat transfer fluid then traverses the external conduit 46 to reach the second end of the packing tower 30. The external conduit 46 can take any shape such that the device 10 can be adapted to operate with any furnace and stack combination. However, in the embodiment shown in FIG. 1, the external conduit 46 includes one or more conduit connectors 48, which allow the conduit to closely follow the shape of the remaining components. In other embodiments, not shown, the external conduit 46 comprises a flexible hermetically sealed passageway. Said external conduit 46 need not be made from a heat resistant material.

The external conduit 46 joins an internal conduit 42 at a conduit junction 44. The internal conduit 42 is exposed to hot exhaust found within the packing tower 30. Depending on the type of fuel being burned, the hot exhaust may be caustic. Consequently, while the external conduit 46 need not be heat and corrosion resistant, preferably, the internal conduit 42 comprises a material that is both heat safe and not subject to corrosion. The internal conduit 42 terminates in the one or more nozzles 40, described above, or other fluid dissemination means, said means proximate the second end of the packing tower 30.

The first end (in this embodiment, the depending end) of the packing tower 30 terminates in the tower to jacket connection point 52. A tower to jacket connection valve 54 is disposed on the heat transfer fluid exit conduit 52 between the first end of the packing tower 30 and the heat transfer jacket 64.

The opposite end of the heat transfer jacket 64 is connected to the pump inlet 56. Consequently, once introduced in the system, heat transfer fluid will circulate same, except for loss through the exhaust aperture 36, when some of the heat transfer fluid is spirited away or otherwise removed by venting exhaust fluid such as cooled flue gas.

While the heat transfer fluid is intended to recycle through the device 10, the system may enter a state when excess fluid is circulating through the system causing a build-up of pressure within the tower. As shown in FIG. 2, a region of the tower interior near the packing tray 37 defines a secondary outlet 80, which functions as an overflow valve. Excess heat transfer fluid that cannot be accommodated by the tower to jacket connection point 52 will exit the system through the overflow valve. While in the embodiment shown, the secondary outlet 80 is shown to be open to the external environment, in other embodiments not shown, the secondary outlet 80 is connected to a collection container for disposal. Further, the heat transfer fluid exiting the secondary outlet 80 may be measured, and the measurement may be used to control the rate of flow of the recirculation pump 50. In instances where the heat transfer fluid is exiting the secondary outlet 80, the recirculation pump throughput is lowered or the pump may even be turned off to maximize heat transfer between the combustion effluent and the temperature transfer fluid. The secondary outlet also serves as a means of egress for liquid products of combustion or condensed products of combustion to exit the economizer. The secondary outlet 80 also allows excess moisture to exit the system. The temperature of the exhaust of the heater may be lowered enough for the moisture within the exhaust to condense and so additional water will be introduced in the tower beyond what was used to transfer heat from the exhaust. Nonetheless, the secondary outlet 80 should not result in emptying of the tower from all liquid such that and the economizer should stay substantially full of heat transfer fluid during its operation, such that secondary outlet 80 serves as the full-point of the device

The device 10 further includes a means to hermetically connect the furnace or boiler to the device 10. As shown in FIG. 2, the device includes a furnace inlet joining plate 82 and a fuel output join plate 88 which allow the device to be removably connected to the furnace or boiler at the first end 60 of the fuel line 66. The outward surfaces of the join plates 82 and 88 are designed to matingly receive opposing flange surfaces of the furnace exhaust connections and fuel inlet connections.

Operation Detail

In operation, at the start of the cycle, the heat transfer fluid is introduced into the recirculation pump 50. In one embodiment, the hot exhaust is introduced only once the tower is filled with the cooling liquid. The fluid is added so that it reaches the tower secondary outlet 80. In this embodiment, the water exiting the secondary outlet 80 signals the filling of the tower. In other embodiments, water continues to be added to the tower until a level-indication float (not shown) is triggered. Other embodiments are capable of functioning in “off duty” cycles where the cooling tower is not filled with water.

In one embodiment, the heat transfer fluid is water; however, other fluids may be employed and are selected to transfer heat efficiently from the exhaust passing through the packing tower 30. Such fluids can comprise substances with boiling points lower or higher than water.

Upon the introduction of the heat transfer fluid, the external conduit 46 is pressurized such that the fluid traverses the internal conduit 42 to charge the nozzle 40. In one embodiment, the external conduit is pressurized to 5 psi. While other pressures are possible and strict pressure control is not necessary, the external conduit should not exceed 30 psi of pressure. In one embodiment, the heat transfer fluid then exits the nozzle 40. In another embodiment, the nozzle 40 incorporates a heat sensor, such that heat transfer fluid does not exit the nozzle 40 until the hot exhaust contacts the nozzle 40.

Concurrently with the heat transfer fluid traversing the internal conduit 42, hot exhaust enters the device 10 through the hot exhaust inlet 20. The hot exhaust permeates the packing tray along with the packing media 32 held by the packing tray, and the exhaust moves upwardly towards the exhaust aperture 36 and away from the hot exhaust inlet 20. In one embodiment, the hot exhaust entering the device 10 through the inlet 20 ranges in temperature from approximately 200 degrees Celsius to 480 degrees Celsius. As the hot exhaust contacts the packing media 32, the hot exhaust transfers some of its heat energy to the packing media 32.

Further cooling of the hot exhaust occurs when the hot exhaust contacts the heat transfer fluid exiting the nozzle 40 as the hot exhaust approaches the nozzle 40. The heat transfer fluid further decreases the temperature of the packing media 32.

Due to this heat exchange, the hot exhaust experiences a temperature decrease of as much as 90% before venting through the exhaust aperture 36. Inasmuch as the heat transfer fluid captures the heat from the hot exhaust, in one embodiment, the heat transfer fluid's temperature increases to approximately 65 degrees Celsius as the heat transfer fluid reaches the packing tray 37, having exited the nozzle 40 and moved through the packing media 32 and packing tray 37, both of which are permeated with hot exhaust.

In an embodiment, the exhaust entered the device 10 through the hot exhaust inlet 20 at a temperature of 200 degrees Celsius. Following the heat transfer process, the heat transfer fluid reached a temperature of approximately 65 degrees Celsius after contacting the hot exhaust and packing media 32. In another embodiment, the heat transfer fluid was at 20 degrees Celsius prior to contacting the media.

While it is impossible to prevent all evaporation of the heat transfer fluid, in one embodiment, heat transfer fluid is added and re-circulated so that the exiting exhaust temperature is maintained to less than 35 degrees Celsius. In this embodiment, the evaporation rate is under 10%. Further, in embodiments where the exhaust temperature is maintained under 49 degrees Celsius the liquid gained from condensation of vapor contained in combustion flue gas will approximately equal the amount of evaporation from the direct contact with the exhaust. As such, the system recuperates any water loss from evaporation of the heat transfer fluid, so as to conserve water resources.

After the heat transfer fluid percolates downwardly through transverse apertures formed in the packing tray 37, it then exits the packing tower 30 through the tower to the heat transfer fluid exit conduit 52. The heat transfer fluid which enters the heat transfer fluid exit conduit 52 contains the heat energy from the hot exhaust and is therefore hot. This heat energy from the heat transfer fluid is transferred, via thermal conductance through the walls of the fuel conduit, to heat the fuel prior to combustion of the fuel.

The heat transfer fluid enters the jacket through the heat transfer fluid exit conduit 52 and contacts the fuel line 66 near the first end 60 of the fuel line 66. In an embodiment of the invented system which conserves energy costs, the fuel entering the system from the first end 60 of the fuel line 66 is not heated up or otherwise thermally pretreated. To the extent that the fuel within the fuel line 66 is from an underground source, such as buried municipal gas lines, the fuel and fuel line 66 are likely to be cold. Even in instances where the fuel originates from an above-ground source such as a truck or tank, the difference in the temperatures between the fuel and the heat transfer fluid will result in a cooling of the fluid to below 21 degrees Celsius. Given the amount of time the cooling fluid contacts the exhaust traversing the tower, in instances where the cooling fluid is below 21 degrees Celsius, the exhaust exiting the tower will be under 32 degrees Celsius. With the exhaust exiting at that temperature, it is possible for the overall heater to run at high efficiency.

This exact temperature is not known and is not a critical design requirement. As long as the exiting exhaust temperature is under 48 degrees Celsius, the fluid temperature leaving the tower is the only required information to properly size the length and width of the fuel heat transfer jacket 64.

As the heat transfer fluid fills the inside of the heat transfer jacket 64, the heat transfer fluid contacts the exterior surface of the fuel line 66. Given the above difference in temperatures, the heat transfer fluid loses its heat energy to the fuel line 66 and to the fuel contained within the fuel line 66 via thermal conductance through the walls of the fuel line. The heat transfer fluid which exits the heat transfer jacket at the pump inlet 56 will approach equilibrium with the temperature of the fuel line 66 at the second end 62 of the fuel line 66. However, since the fuel at the second end 62 of the fuel line 66 has most recently entered the device 10, this fuel is at the lowest temperature given its recent decompression from distribution line pressures. Consequently, the heat transfer fluid will reach or approximate its equilibrium point as it exits the heat transfer jacket 64 through the pump inlet 56.

The heat transfer fluid which reaches the recirculation pump 50 is pressurized to between 5 psi to 30 psi and forced out of the pump outlet 58 starting the cycle again by traversing the external conduit 46.

At the end of the operation of the furnace or boiler, or when it is desirable to flush the system clean, the heat transfer fluid is collected. The fluid may be collected through several points, including at the recirculation pump 50. At the recirculation pump 50, the heat transfer fluid may be diverted away from the device 10 by directing the fluid to a secondary outlet (not shown) instead of the pump outlet 58. Alternatively, the tower to jacket connection valve may be closed. Given this eventuality the heat transfer fluid will congregate and exit the device 10 through the packing tray secondary outlet 80 depicted in FIG. 2.

In the event of loss of heat transfer fluid, it may be replenished by the introduction of additional heat transfer fluid at the recirculation pump 50.

The device 10 also allows for several points of control. If the hot exhaust exiting the exhaust aperture 36 is too cold, it is possible to decrease the flow out of the nozzle 40 through operation of a valve at a conduit junction 44. The valve may be automatically controlled, via thermostat, or hand-controlled. Similarly, if the fuel exiting the fuel line 66 at the fuel line first end 60 is still too cool, the rate of flow of the heat transfer fluid may be adjusted at the tower to jacket connection valve 54 such that the fluid flow is increased around the exterior of the fuel conduit.

Air Induction Assembly

Turning to the alternate embodiment of the economizer system depicted in FIG. 3, the fan blower alternate embodiment 110 depicted therein does not seek to transfer heat energy to boiler fuel. Instead, the principal purpose of the alternate embodiment 110 is to ensure that the connected boiler receives a sufficient oxygen supply. Providing a sufficient oxygen supply is especially important for boilers having natural draught burners which in normal operation—i.e. operation where the boiler is not connected to an economizer—rely on air supply from the stack to maintain the flame. If an economizer is introduced to the stack, the exhaust is cooled and does not rise out of the stack. The trapping of the exhaust prevents the draught from pulling in outside air to the boiler's burners starving same of oxygen.

The embodiment 110 shown in FIG. 3 is designed to use an economizer with a natural draught boiler or any other fuel burning appliance which requires air from the exhaust to maintain the flame at the burners. The economizer 110 comprises a packing tower 130 having a first end 134 and a second end 135. A hot exhaust inlet 120 extends from the packing tower 130 at a location intermediate the two ends 134,135. Preferably, as shown in FIG. 3, the hot exhaust inlet 120 is located one third of the length of the packing tower 130 from the packing tower first end 134 and two thirds of the length of the packing tower 130 second end 135.

The hot exhaust inlet 120 comprises a heavy duty metal conduit, in one embodiment. The hot exhaust inlet 120 must withstand high temperatures and pressures of boiler exhaust traversing the inlet 120. A hot exhaust inlet aperture 162 is defined within the inlet 120 to allow for removal of excess fluid from the inlet 120. In one embodiment, the excess fluid is drained by gravity; in another embodiment, a pump is reversibly attached to the aperture 162 to remove fluid. The hot exhaust inlet 120 is angled with the end closest to the packing tower 130 lower than the end of the inlet 120 which is connected to the boiler. Given the angle, should excess fluid build up in the packing tower 130, the fluid will not traverse the inlet 120. Such fluid forms due to the cooling action of the economizer on the exhaust. If the condensation from the exhaust or other fluid were to return to the burners via the inlet 120, the burner flames can be extinguished.

In yet another embodiment, the aperture 162 is also used for reversible mounting of sensors (not shown) and for other means of monitoring the presence of exhaust within the hot exhaust inlet 162. In one embodiment, a switch (not shown) is mounted within the aperture 162, said switch being connected to the blower fan assembly 180 described fully below.

As the hot exhaust exits the inlet 120 and enters the packing tower 130, it contacts the overflow lines 160. The overflow lines 160 are connected to the packing tower 130 at the upper overflow aperture 161 near at the first end 134 of the packing tower 130. In one embodiment, the side of the packing tower incorporates a sight gauge tube 165 comprising clear tubing connected to the lower aperture 163 and the upper aperture 161. The sight gauge tube 165 allows for viewing of the level of liquid build-up within the packing tower 130. Any excess fluid that builds up within the packing tower 130 will fall down due to gravity towards the first end 134 of the packing tower 130. Initially, such fluid will exit the packing tower by being directed through the lower 163 aperture to the external sight gauge tube 165. However, if the amount of fluid becomes critical, and at the level of the exhaust inlet 120, the excess fluid will also exit through the upper aperture 161. In one embodiment, when the condensed exhaust fluid exits from the upper aperture 161, a sensor is triggered, indicating excess fluid in the packing tower 130. In another embodiment, when the fluid exits the upper aperture 161, the economizer cycle is slowed down by directing less exhaust through the inlet 120. Any fluid exiting the upper overflow aperture 161 is directed by the overflow lines 160 away from the device 110. The overflow lines 160 are angled to prevent the fluid from exiting the economizer in multiple directions.

After the hot exhaust enters the packing tower 130, the hot exhaust moves away from the first end 134 of the packing tower 130 towards the second end 135 of the packing tower 130. The interior of the packing tower between the inlet 120 and the second end 135 contains packing media (not shown). The packing media is inserted and removed by accessing the interior of the packing tower 130 via the packing media access portal 164. During operation of the economizer 110, this portal is sealed; however, if any of the media becomes deformed and is no longer able to function, it can be replaced by accessing the interior of the packing tower 130 through this access portal 164.

The packing media is cooled by being showered by a heat exchange fluid exiting the nozzle 140. The nozzle 140 is connected to the exterior of the packing tower 130 via an internal conduit 142. The internal conduit is in turn connected to an external conduit 146. In one embodiment, both the internal conduit 142 and the external conduit 146 comprise the same material; in other embodiments, the two conduits are made of different material, with the external conduit 146 being made from a less resistant material given that it is not exposed to the exhaust within the packing tower 130.

The external conduit 146 is connected to a cold fluid inlet (not shown). In one embodiment, the cold fluid inlet is connected to a heat transfer jacket, as was shown in FIGS. 1 and 2. In another embodiment, the cold fluid inlet is connected to a fresh supply of cooled fluid, such as a cold water line or a cooling body of water.

As the fluid exits from the nozzle 140, it traverses the packing tower 130 towards the first end 134 of the tower 130. The flow rate of the fluid out of the nozzle 140 is set based on the stack temperature read by temperature sensor 172. During operation, the fluid rate is set to maintain a constant temperature at 172 so that any water captured from the combustion process will be evaporated. The flow rate will vary to maintain this temperature by changing the speed of the pump 150.

As can be best seen in FIG. 6, fluid from the packing tower 130 is collected and conveyed to the recirculation pump 150 via the pump's inlet 156. The inlet 156 is connected to the packing tower 130 via a pump to packing tower connection pipe 270. The pump to packing tower connection pipe 270 is in fluid communication with the first end 134 of the packing tower 130. In the embodiment shown in FIG. 6, the pump to packing tower connection pipe 270 is closer to the first end 134 than the lower aperture 163. Therefore, fluid will not reach the lower aperture 163 except unless insufficient quantity of fluid is being conducted from the packing tower 130 via the pump to packing tower connection pipe 270. In one embodiment, if fluid is detected to have exited the lower aperture 163, the pump 150 output is increased.

The recirculation pump 150 forwards the heat exchange fluid under pressure to the pump outlet 158. The pump outlet 158 is connected to a heat exchange jacket as shown in FIGS. 1-2 or other heat exchange means, such as an outdoor fluid cooling body. In another embodiment, the output of the recirculation pump 150 is discarded.

After passing over the fluid exiting the nozzle 140, the exhaust exits the tower 130 by means of an exhaust aperture 136 located at the second end 135 of the tower 130. The aperture 136 provides for fluid communication between the tower 130 and the economizer exhaust stack 170. As the exhaust enters the exhaust stack 170, it has been considerably cooled by the packing media and the heat exchange fluid from the nozzle 140. If the exhaust has begun to condensate, fluid will fall down the packing tower 130 towards the first end 134. A temperature sensor 172, measures the temperature and rate of exhaust exiting the second end 135 of the packing tower 130 and adjusts the fluid flow of the nozzle 140 to prevent excess condensation given the likely make up of the exhaust.

An air induction unit, described below, is also connected to the exhaust stack 170.

Induction Unit

In the embodiment shown in FIG. 3, the air induction unit is connected to the economizer exhaust stack 170. In the embodiment shown in FIG. 5, the induction unit is connected to the inlet 120. The placement of the induction units at either location ensures that sufficient air is introduced into the system to maintain combustion within the boiler.

The induction unit comprises two components, one internal to the exhaust stack 170 and another exterior to the exhaust stack 170. The interior assembly comprises a pipe having two segments, a straight segment 174 and a curved segment 176. The straight segment 174 has a first end which is open while the second end of the straight segment 174 is connected to the curved segment 176. The curved segment 176 in turn is connected to the external assembly. The straight segment 174 is enclosed by the exhaust stack 170. The straight segment 174 is parallel to the exhaust stack, such that the interior 175 of the straight segment is concentric to the exhaust stack 170, as depicted in FIG. 4.

While as shown in the cut-away view of FIGS. 3 and 4, the straight segment 174 and the economizer exhaust stack 170 are substantially cylindrical in shape, other shapes may be used in other embodiments. In another embodiment, not shown, a rectangular vent is used for the exhaust stack 170.

The introduction of pressurized exterior air to the interior 175 of the straight segment 174 creates a pressure differential between the interior 175 of the straight segment 174 and the interior 177 of the exhaust stack 170. In one embodiment this pressure differential is set according to the boiler burner type and emission requirements. The pressure differential causes a partial vacuum to form in the interior 177 of the exhaust stack 170 surrounding the straight segment 174. This vacuum pulls air in from the outside of the exhaust stack 170 down through the exhaust stack 170 to the packing tower 130 and eventually to the boiler via the inlet 120.

The change in pressure in the straight segment 174 originates with the blower fan assembly 180 connected to the curved segment 176. The blower fan assembly 180 comprises a blower motor 182. The motor 182 operates a fan (not shown) which draws air in from the exterior of the economizer 110 through an air intake in the blower fan assembly 180.

Inasmuch as the fan draws exterior air into the curved segment 176, the fan does not contact the potentially caustic exhaust contained within the exhaust stack 170. Therefore, the fan does need not comprise durable materials. In one embodiment the amount of air the fan introduces into the stack per minute is set to meet boiler burner air needs and any emissions requirements. In one embodiment, the fan speed is kept constant throughout the operation of the system. In another embodiment, the fan speed and resulting output is automatically calculated and set on the basis of the exhaust sensor attached to the hot exhaust monitor aperture 162. In another embodiment, the fan is automatically turned to full speed as soon as exhaust is detected within the system. In yet another embodiment, the speed of the fan is set by the temperature of the flames within the boiler, said temperature being an indication of whether the flames have sufficient air.

The life span of the fan within the fan assembly 180 is maximized in this embodiment inasmuch as the fan does not contact the cooled exhaust and the condensate products within the exhaust. The condensation is instead collected and removed at the first end 134 of the packing tower 130. A fan connected directly to the humid environment of the packing tower 130 would suffer from the effects of contact the caustic environment.

Exhaust Intake Cooling

An alternate embodiment of the economizer is depicted in FIG. 5. The economizer 210 comprises a hot exhaust inlet 220 connected to a boiler (not shown) and a packing tower 230. The packing tower 230 used with this alternate embodiment 210 is analogous to the packing towers described above.

A testing port 262 is defined in the hot exhaust inlet 220 at a point along the length of the hot exhaust inlet between the boiler connection and the air induction segment 222. In one embodiment, a temperature gauge is connected to the testing port 262, while in another embodiment a combustion analyzer is connected at the testing port 262. In one embodiment, the combustion analyzer is used during setup or commissioning of the burner. During this setup phase, air and gas ratios are set to the proper amount, to ensure a clean burn. The analyzer is removed from the system after the setup is completed. During operation, temperature is measured to maintain the air mixture setting determined during the setup phase. In one embodiment, the hot exhaust inlet 220 air induction segment 222 is a stand-alone portion of the hot exhaust inlet 220 that can be connected to the hot exhaust inlet 220 in the event that the additional air supplied by the system is needed. In another embodiment, the induction segment 222 is integrally molded into hot exhaust inlet 220, but can be bypassed if not needed by closing the fan valve connection 223.

A fan assembly 224 is connected to the induction segment 222. The fan assembly comprises a fan 226, the fan housing 228, and the air introduction tube 232. In one embodiment, the fan 226 is protected by the fan housing 228, but at least one side of the fan 226 is exposed to the exterior atmosphere allowing the fan to draw in air from the atmosphere into the interior of the fan housing 228.

The interior of the fan housing 228 is connected to the air introduction tube 232. The fan valve 223 is found on the fluid connection between the fan housing 228 and the air introduction tube 232. In one embodiment, the fan valve connection 232 is automatically closed when exhaust is detected in the air introduction tube 232. Therefore, the fan 226 is protected from the hot exhaust in the inlet 220. If the fan is blowing air into the system, the valve 223 may be open inasmuch as the pressure of the air coming from the fan will push back and protect the fan from any returning exhaust. The exhaust will instead be directed to the packing tower 230 found at the opposite end of the inlet 220.

The air introduction tube 232 connects the fan valve 223 to the interior of the inlet 220. In one embodiment, a portion 234 of the introduction tube 232 is substantially parallel with the air induction segment 222 of the inlet 220. A connected portion 236 of the induction tube 232 turns approximately 90 degrees and becomes substantially perpendicular to the air induction segment 222.

When the fan 226 is turned on, air is forced from the external atmosphere into the fan housing 228. Inasmuch as the fan valve connection 223 is open, the air passes through the fan housing 228 to the air introduction tube 232 first the perpendicular segment 236 and then the parallel segment 234. The parallel segment 234 is open to the interior of the inlet 220. When the air exits the parallel segment 220, a partial vacuum is formed at the vacuum portion 238 of the inlet 220. The vacuum portion 238 surrounds the open end of the segment 228 between the exterior walls of the parallel segment 234 and the interior walls of the inlet 220.

The air added to the inlet 220 functions to decrease the temperature of the exhaust found in the inlet 220. A lower temperature of the exhaust allows the economizer to be used with high-temperature exhaust boilers. Further, the lower temperature of the exhaust allows for use of a cooling liquid other than water. In one embodiment, the cooling fluid comprises ethylene glycol or propylene glycol or a mix of either and water. The introduction of either ethylene glycol or propylene glycol allows the economizer to be maintained in a ready with all lines charged with cooling fluid, even when the economizer is shut down in climates where freezing occurs. These liquids would not be feasible or safe to use if the exhaust was of a high temperature.

The speed of the fan 226 is adjusted depending on the amount and temperature of the exhaust in the inlet 220. A temperature and pressure sensor 240 is located on the length of the air induction segment 220 between the boiler connection and the fan assembly 224 connection.

As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 

1. A flue gas heat recovery device comprising: a. a packing tower adapted to receive a flue gas stream; wherein said packing tower contains at least one water inlet, a water collection reservoir and a packing tray positioned intermediate said water inlet and said reservoir; b. a fuel conduit in thermal communication with the reservoir, wherein the fuel conduit has a first end in close spatial relationship to a first end of said reservoir, and a second end in close spatial relationship to a fuel supply point; c. a fluid conduit having a first end in fluid communication with an exterior surface of the fuel gas line and a second end in fluid communication with said water inlet; and d. at least one fan connected to the packing tower.
 2. The flue gas heat recovery device of claim 1 wherein said packing tower comprises a vertically-oriented cylinder.
 3. The flue gas heat recovery device of claim 1 wherein said packing tower is adapted to be integrated into a stack.
 4. The flue gas heat recovery device of claim 1 further comprising a recirculation pump in fluid communication with said water inlet.
 5. The flue gas heat recovery device of claim 1 wherein said water inlet further comprises a nozzle.
 6. The flue gas heat recovery device of claim 1 wherein said packing tower further comprises a combustion gas inlet positioned proximate to said packing tray.
 7. The flue gas heat recovery device of claim 1 wherein thermal communication between the fuel gas line and the reservoir comprises a heat transfer jacket.
 8. The flue gas heat recovery device of claim 7 wherein the heat transfer jacket comprises an external surface wherein said external surface is insulated and an internal chamber wherein said fuel gas line traverses the internal chamber.
 9. The flue gas heat recovery device of claim 1 wherein the packing tower, the fuel line, and the fluid conduit form a closed-loop system.
 10. A method for recovering heat from flue effluent, the method defining a heat recovery cycle comprising: a. contacting the effluent with a heat transfer fluid for a time sufficient to transfer heat from the effluent to the heat transfer fluid; b. introducing air into the effluent to decrease the temperature of the effluent and to improve combustion; c. transferring heat from the now heated heat transfer fluid to a fuel gas so as to heat the gas and cool the heat transfer fluid; d. combusting the now heated fuel gas which leads to the production of additional flue effluent; and. e. returning to step (a) utilizing the now cooled heat transfer fluid and the additional flue effluent.
 11. The method for recovering heat from flue effluent of claim 10, wherein said heat transfer fluid comprises water.
 12. The method for recovering heat from flue effluent of claim 10, wherein said heat transfer fluid is exposed to sufficient effluent to reach the temperature of about 65 degrees Celsius.
 13. The method for recovering heat from flue effluent of claim 10, wherein said transferring of heat from the heated heat transfer fluid to a fuel gas occurs in a heat transfer jacket without direct physical contact of the fuel gas and the heat transfer fluid.
 14. The method for recovering heat from flue effluent of claim 10, wherein said heat transfer fluid is reused in multiple cycles.
 15. A method for recovering heat from flue effluent to maintain stable temperatures during pressure changes, the method defining a heat recovery cycle comprising: a. contacting the effluent with a heat transfer fluid for a time sufficient to transfer heat from the effluent to the heat transfer fluid; b. introducing air to the effluent to decrease the temperature of the effluent and to improve combustion; c. transferring heat from the now heated heat transfer fluid to a fuel gas line so as to heat the gas line and cool the heat transfer fluid; d. combusting further fuel to produce additional effluent; and. e. returning to step (a) utilizing the now cooled heat transfer fluid and the additional flue effluent.
 16. The method for recovering heat from flue effluent of claim 15, wherein said fuel gas line receiving heat from the heat transfer fluid is a high pressure gas line.
 17. The method for recovering heat from flue effluent of claim 16 wherein said high pressure gas line contains fuel at 1200 psi.
 18. The method for recovering heat from flue effluent of claim 15, wherein said fuel gas line receiving heat from the heat transfer fluid is a low pressure gas line.
 19. The method for recovering heat from flue effluent of claim 18, wherein said low pressure gas line contains fuel at 80 psi. 